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Selective hydrogenation of crotonaldehyde over Pt catalysts
Author: WangXiaoXia
Tutor: LuoMengFei；XieGuanQun
School: Zhejiang Normal University
Course: Physical and chemical
Keywords: Crotonaldehyde The Pt catalyst Lewis acid Electronic effects Pt particle size
CLC: O643.32
Type: Master's thesis
Year: 2010
Downloads: 57
Quote: 1
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Abstract
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α, β-unsaturated aldehydes are prepared spices, pharmaceuticals and other chemical products, an important starting materials and reaction intermediates. By vapor phase selective hydrogenation of α, β-unsaturated aldehydes is a low-pollution, high value-added approach. Papers prepared by impregnation Pt-based catalysts was investigated selective hydrogenation of crotonaldehyde catalyst performance. Combined with X-ray powder diffraction (XRD), CO chemisorption, NH3 temperature programmed desorption (NH3-TPD), in situ infrared reflectance spectroscopy (DRIFTS) and in situ X-ray photoelectron spectroscopy (XPS) characterization results. Found Pt/NaCl/ZrO2 catalyst not only has a high selectivity of crotyl alcohol, and has a higher activity. Active sites and the reaction mechanism was studied in detail. The results are as follows: 1.NaCl right Pt/ZrO2 selective hydrogenation of crotonaldehyde catalyst performance by preparing and comparing a series of NaCl vapor phase catalyst modified Pt/ZrO2 selective hydrogenation of crotonaldehyde, the activity of the catalyst was observed with the increase of NaCl concentration, selectivity to crotyl alcohol content of 1% NaCl that there is a maximum of 60%. NH3-TPD and pyridine infrared characterization results showed that the catalyst surface Lewis acid strength increases with the decrease of NaCl, which is the cause of elevated activity of the catalyst. CO adsorption and in situ DRIFTS situ XPS results showed that the catalyst Pt particle surface electronegativity increases can improve the selectivity of crotyl alcohol. However, when the content exceeds 3% NaCl, crotyl alcohol selectivity begins to decline. Therefore, the growth Pt particles, leading to the interface between Pt and the carrier and carbonyl adsorption decrease is caused by the decrease in selectivity main crotyl alcohol. (2) Additives NaOH for hydrogenation of crotonaldehyde Pt/ZrO2 catalyst performance comparison selection Zr02 chlorine and chlorine-ZrO2 (Cl) as a carrier of NaOH added to a detailed study of the role. Found that the presence of Cl ions, enhances the strength of the Lewis acid, Na ions alter the electron density of the catalyst, the main reason affecting the performance of the catalyst. Found that adding NaOH, the Cl-containing catalyst and its activity and selectivity of the target product crotyl alcohol were significantly improved; contrary C1 catalysts without catalytic performance. 3. Pt/NaCl/ZrO2 and Pt/CeO2 gas catalyst deactivation selective hydrogenation of crotonaldehyde Mechanism using deposition-precipitation method and the impregnation method were prepared Pt/CeO2 and Pt / NaCl (1) / ZrO2 catalyst, the catalyst selective hydrogenation of crotonaldehyde properties were compared, focusing on the two catalyst deactivation were compared. Found that the catalyst activity decreased during Pt/CeO2 accompanied crotyl alcohol selectivity decreased; while Pt/NaCl/ZrO2 catalyst activity decreased along with the process of crotyl alcohol selectivity increased. Found, Pt/CeO2 catalyst reduction state during the reaction Ce3 gradually transformed into Ce4, accompanied by the surface carbon deposition; while no element exists Pt/NaCl/ZrO2 catalyst reduction and oxidation of the surface of the carbon deposition occurs. This has contributed to changes in selectivity for different reasons.
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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Chemical kinetics,catalysis > Catalytic > Catalytic reaction
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